It has previously been suggested to use a plurality of modulated laser or light beams for scanning a recording medium so that a plurality of lines is simultaneously recorded on the recording medium. Examples of this type of apparatus are disclosed in U.S. Pat. No. 5,426,528 to Yamamoto et al, U.S. Pat. No. 5,576,852 to Sawada et al, and U.S. Pat. No. 5,578,819 to Kataoka et al.
The use of a plurality of laser beams enables the throughput of a laser printer, for example, to be increased. With a print resolution of 600 dots per inch (dpi) in both scan and process directions (the present industry standard), a process-direction laser beam separation of 42 .mu.m must exist. This separation, along with the optical magnification of the system, produces a spacing and tolerance between lasers not practical or desirable in manufacturing a semiconductor laser array.
Accordingly, a semiconductor laser array is manufactured to reasonable tolerances and then tilted until the required process-direction spacing of 42 .mu.m for 600 dpi is achieved. This tilting results in the lasers in the array no longer being aligned vertically. Therefore, the tilt of the array produces a separation in the scan direction between each of the laser beams so that one laser beam leads the other beams as they sweep across a recording medium such as a rotating photoconductor drum, for example.
Changes in beam separation in a multi-beam scan can occur due to temperature, laser power, mirror facet variation (speed of mirror motor, configuration of facets of mirror, and other periodic events involving the mirror), or other variables. When the separation drift occurs, image distortion on the rotating photoconductor drum can occur.